1. Field of the Invention
The present invention relates to a method of manufacturing a micro flux gate sensor.
2. Description of the Related Art
A fluxgate sensor is a device that detects magnetic energy, which is not perceivable by human sense organs. Such a magnetic detection sensor may be used in applications that require detection of magnetic energy formed around a circumference. For example, these applications may include position identification of airplanes, vessels and vehicles, motion detection in a virtual reality space, geomagnetic compensation and dot noise compensation for high definition television (HDTV), magneto-encephalograph and magneto-cardiograph measurement acquisition in a medical device, and many others.
Recently, since the fields of application have gradually spread, there has been a trend toward providing devices that are thinner, lighter and less expensive. Correspondingly, there has been a trend toward providing a fluxgate sensor that is thinner, lighter and less expensive.
A micro fluxgate sensor primarily includes a core made of soft magnetic material, an excitation coil wound around the core for inducing a magnetic field when a current is applied thereto, and a magnetic field detecting coil for detecting the effect of an external magnetic field on the magnetic field induced by the excitation coil. A basic detecting principle utilizes a nonlinear characteristic of the soft magnetic core, i.e., a saturation characteristic. If a proper alternating current (AC) is applied to the excitation coil to induce the magnetic field, flux density in the core is periodically saturated. At that time, if the external magnetic field to be measured is applied, the flux density of the core varies. The magnetic field detecting coil measures a variation of the flux to determine a dimension, either strength or direction, of the external magnetic field.
In order to manufacture a micro fluxgate sensor, a coil is generally wound around a large, bar-type core or a ring-type core of a soft magnetic ribbon. Accordingly, the core itself becomes relatively large thereby enlarging its volume and increasing the manufacturing cost of the core. In addition, since the flux variation generated by the excitation coil and the detected magnetic field do not prevent flux leakage due to the core, highly sensitive detection of the magnetic field is not readily achieved.
Therefore, various methods of manufacturing a flux gate sensor by using a MEMS technique have been studied and developed.
For example, a first seed layer is formed on a wafer and a metal material is plated according to a certain pattern on the first seed layer to form a lower coil. A first insulation layer is formed on the lower coil and a core layer of magnetic material is formed at a position corresponding to the lower coil, on the first insulation layer. Then, a second insulation layer is formed to cover the core layer, and the first and the second insulation layers are etched to form a viahole so as to expose the lower coil.
Then, a second seed layer is formed on the viahole and the second insulation layer and a metal material is plated according to a certain pattern on the second seed layer to form an upper coil. Since the viahole is filled with the metal material, the upper coil and the lower coil are electrically connected. A third insulation layer is formed to cover the upper coil. According to this process, a flux gate sensor is manufactured.
However, according to the conventional method of manufacturing the flux gate sensor, it is impossible to measure whether the viahole is formed to open to the lower coil because the size of the viahole is too small. Accordingly, the lower coil and the upper coil may not be electrically connected although the seed layer is formed on the viahole and the viahole is filled with the metal material.
If the viahole is formed too large in view of the above disadvantage, the metal material filling neighboring viaholes comes into contact with each other to generate defects.